Daring jumps, skilful twists and skilful landings: squirrels are not only anatomically perfectly adapted to life in treetops. They also have special decision-making and learning abilities that allow them to perform impressive maneuvers when jumping from branch to branch. Scientists report this in the journal Science.
Squirrels spend most of their time high up in the trees – an unpredictable environment in which they move nimbly in a maze of branches, nesting and dodging predators. Mistakes in this habitat can result in fatal falls. How the animals learn to estimate and adapt their movements in fractions of a second in order to avoid such mistakes has not yet been fully clarified.
To get to the bottom of this question, researchers at the University of California built an obstacle course in a campus eucalyptus grove that contained various rigid and flexible artificial branches. From these, wild fox squirrels (Sciurus niger), a separate species within the genus of squirrels, could jump off to get a peanut. The distance between the jumping branch and the treat varied.
In their experiments, the scientists did not only want to better understand the abilities of the animals: rather, the basis for the development of robots should be created, which can move quickly through different terrain, such as the rubble of a collapsed building.
“As a model organism for understanding the biological limits of balance and agility, I think squirrels are second to none,” explains biomechanist Nathaniel Hunt. “By trying to understand how squirrels do it, we may be able to discover general principles of high-speed locomotion in canopy and other complex terrains that also apply to the movements of other animals and robots.”
As expected, as Hunt and biologist Robert Full found, the fox squirrels were more cautious the weaker or more pliable the branch was. However, it only took them a few tries to get used to the different levels of flexibility.
“When they jump a distance, they decide where to jump off based on a trade-off between the flexibility of the branch and the size of the gap they have to jump over,” says Hunt. “And when they hit a branch with new mechanical properties, they learn to adjust their starting mechanics in just a few jumps. This behavioral flexibility, adapting to the mechanics and geometry of the jump and landing structures, is important to accurately jump over a gap and land on a small target.”
The flexibility of the branch was six times more important for the animals’ jump decision than the distance to be jumped. According to Hunt, this could be because the squirrels rely on their sharp claws. In fact, not a single one of them fell during the tests.
This picture keeps animal lovers on Twitter and Facebook busy. A bad Photoshop joke? no Apparently the sloppy mother of the young squirrels was to blame for the dilemma. But see for yourself.
Source: WORLD / Sebastian Struwe
“If they jump into the air with too much or too little speed, they can use a variety of landing maneuvers to compensate,” he explains. “If they jump too far, they roll forward around the branch. If they jump too short, they will land on their front legs and swing under the branch before pulling themselves up. This combination of adaptive planning behavior, learning control, and reactive stabilization maneuvers helps them move quickly through the branches without falling.”
In addition, the squirrels showed unexpected innovative abilities: When performing difficult jumps, they realigned their bodies and, during the jump, also pushed themselves off a back wall in the experimental setup, which actually had no function in the experiment. This reminded the researchers of the sport of parkour, in which people jump or swing over obstacles quickly and without tools.
In an explanatory contribution to the study, the two neuroscientists Karen Adolph and Jesse Young, who were not involved in the analysis, are impressed: With their work, the authors have provided a remarkable demonstration of the creativity of functional movement by showing “that wild squirrels jump on the Coordinate the bending of branches and the distance to the target, even inventing ingenious maneuvers if necessary”.
Just as movement in the real world requires flexibility and creativity, scientists studying natural locomotion must be as imaginative as their natural animal subjects, write Adolph and Young in Science: “The art is in understanding movement in all its complexity and at the same time to ensure sufficient experimental control and measurement accuracy.” The study is a good example of this.
This article was first published in August 2021.
